Conventional toothbrushes generally include tufts of bristles mounted on the head of an oral brush handle. One method of manufacturing toothbrushes involves placing tufts of finished (end-rounded) bristles so that their unfinished ends extend into a mold cavity, and forming the toothbrush body around the unfinished ends of the tufts by injection molding, thereby anchoring the tufts in the toothbrush body. The tufts are held in the mold cavity by a mold bar having blind holes that correspond to the desired positioning of the tufts on the finished brush. The finished bristles may be formed by a process that includes unwinding a rope of filaments from a spool, end-rounding the free end of the filaments, cutting off a portion of the rope that is adjacent the free end of the filaments to form bristles having the desired length, and placing the bristles into a rectangular box, called a magazine. Tufts are then formed by picking groups of bristles from the magazine.
However, problems often occur when bristles are picked from the magazine and transferred to the machine that fills the moldbar. A picker device attempts to repeatedly choose the proper number of bristles to form a tuft. However, the inherent difficulty in this task may result in tufts of bristles that are either too small or too large for the blind holes in the moldbar. If a tuft is too small, the blind hole is not sufficiently filled and plastic will flow into the hole when the handle is formed. If a tuft is too large, one or several bristles may not enter the moldbar, but rather curl to the side and prevent the complete insertion of the tuft into the moldbar, which may then interfere with molding.
These problems can be addressed by filling the moldbar with continuous filament bunches supplied directly from spools. Methods and machines used to fill moldbars from a continuous filament stream is described in U.S. patent application Ser. No. 09/863,193, entitled TUFTING ORAL BRUSHES, the disclosure of which is incorporated herein by reference. Toothbrushes using these methods can be manufactured relatively easily and economically by an injection molding process that includes advancing free ends of strands of continuous filaments into a moldbar. The filaments are not cut to bristle-length until after the free ends of the filaments have been advanced into the holes in the moldbar, thus reducing or eliminating the problems that tend to occur when handling cut tufts, as discussed above.
Problems may arise, however, when supplying the spool fed tufting machine due to catenary problems inherent in the spools of continuous filaments. Problems include non-uniform tension and length between individual filaments, which are generally the result of the filament manufacturing process. These tension and length differentials may cause individual filaments to eventually loop as the filament bundle is pulled from the spool, as shown in FIGS. 1A–1D, or wrap around the bundle, as shown in FIG. 2.
When these problems occur, the dimensions of the filament bundle entering the feeding device of the spool fed tufting machine may vary. For example, when filaments twist around each other, the diameter of the entire bundle increases. Since the tolerances on the feeding device are generally tight, the area of the bundle with the increased diameter may not fit into the feeding device. The area of increased diameter also may not fit into the blind holes of the moldbar.
Further, when individual filaments have little tension, those filaments tend to slide axially relative to the other filaments, back in the direction of the spool during feeding. As the individual filament continues to be moved back towards the spool, and the slack increases, a loop may eventually form. This loop may eventually snag or break the filament.